This application for competitive renewal is submitted by a multi-disciplinary team of senior investigators who propose to continue their studies on bioactive factors in human milk. Our program project is unique in its focus on human milk and the mechanisms by which human milk protects infants against infectious disease. The respective projects of this renewal consider the role of human milk in protection against human caliciviruses; rotavirus; campylobacter and related pathogens; enteropathogenic E. coil and related pathogens; and stable toxin (ST) of E. coil. The project protocols utilize in vitro assays, animal models, and human subjects, and are supported by interaction with cores that address epidemiology, biostatistics and translational research; glycobiology and synthetic chemistry; and molecular biology. In this application for renewal, we propose to examine protection against multiple pathogens through fundamental mechanisms of innate and adaptive immunity that are expressed in human milk, specifically, oligosaccharides and related glycoconjugates, and secretory antibody. This overall theme will be addressed by studying the extent to which these human milk factors inhibit pathogen-cell surface binding and provide cross-protection against multiple pathogens. We also will examine the genetic basis for variability in expression of oligosaccharide protective factors in human milk and infant susceptibility to diarrheal diseases. Based on results of studies conducted in the current grant cycle, this renewal will involve synthesis of oligosaccharides found in human milk and translational research that tests their protective efficacy in pre-clinical studies that lead to carefully designed phase I and II trials in young children.